Method For Cleaning Wafers Using A Polycarboxylate Solution

ABSTRACT

A cleaning solution and method for removing submicron particles from the surface and/or the bevel of an electronic substrate such as a semiconductor wafer. The cleaning solution comprises a polycarboxylate polymer or an ethoxylated polyamine. The method comprises the step of contacting a surface of the substrate with a cleaning solution comprised of a polycarboxylate polymer or an ethoxylated polyamine. Additional optional steps in the method include applying acoustic energy to the cleaning solution and/or rinsing the surface with a rinsing solution with or without the application of acoustic energy to the rinsing solution.

This application claims the benefit of U.S. patent application Ser. No.12/330,486, filed Dec. 8, 2008, which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

The manufacturing of devices on semiconductor wafers consists of variousrepetitive steps, such as deposition of layers, etching of layers,polishing of layers, deposition and photolithography of photoresistlayers and so on. After some of these steps, and when various parts orstructures of the final device on the wafer are exposed, thesemiconductor wafers need to be cleaned to remove particles which mayhave deposited during such various processing steps and before the nextlayer is deposited. As presently practiced, particle removal is usuallyachieved by a combination of mechanical and chemical mechanisms. In manywafer fabs, special dedicated tools are being used to scrub or removeparticles, often called scrubbers. In many such scrubbers a mechanicalparticle removal method is used simply with room temperature orsometimes-heated DI (deionized) water. Chemicals can be added to enhancethe removal efficiency. Cleaning tools differ from scrubbers in thatmechanical removal techniques are combined with chemicals instead ofsimple DI water to remove particles both with a mechanical method and achemical method combined. Additionally in a cleaning tool, otherfunctions can also be performed in addition to particle removal. E.g.removal of metallic impurities, organic impurities and even wet etchingof Si₃N₄, SiO₂, poly-Si, Ni, Co, Ti, TiN or other layers and wetstripping of photoresist can be performed in a cleaning tool in additionto the particle removal function that is the object of this invention.

In a cleaning tool for semiconductor wafers, the most popularcombination to remove particles is a combination of megasonics vibrationtogether with a liquid mixture of NH₄OH, H₂O₂ and H₂O in which thewafers are immersed or with which the wafers are covered. The megasonicssystems commonly used in the semiconductor industry use frequenciesclose to or about 1 MHz (one megahertz).

Before the invention of megasonics, ultrasonics was used. Ultrasonicshas frequencies in the range of 20 kHz to about 120 kHz. However, sincethe invention of megasonics, ultrasonics is rarely used on semiconductorsubstrates because of the damage potential at frequencies in the rangeof 20 kHz to about 120 kHz. Hence, megasonics with frequencies close toor about 1 MHz is the current state of the art for semiconductorsubstrates.

The most popular chemistry conditions used for particle removal togetherwith megasonics on semiconductor wafers, a liquid mixture of NH₄OH, H₂O₂and H₂O, is a part of the so called RCA cleaning sequence originallydeveloped by W. A. Kern and D. A. Puotinen, at the RCA company in 1965,and published in 1970, RCA Rev., 31, pp. 187-206 (1970). The traditionalRCA cleaning sequence consists of 2 steps, the SC-1 step (StandardClean-1 step) and the SC-2 step (Standard Clean-2 step). Specifically,the particle removal function of this RCA sequence is carried out by theSC-1 step of the RCA cleaning cycle. The SC-1 is also sometimes calledthe APM (Ammonia Peroxide Mixture) step. The SC-1 step (StandardClean-1) is mainly aimed at removing particles while the SC-2 step(Standard Clean-2) is mainly aimed at removing metallic contamination.The SC-1 step consists originally of a 1/1/5 mixture of NH₄OH (28-30%strength as NH₃-w)/H₂O₂ (29-31% strength as H₂O₂-w)/DI (De Ionized)water at 70° C. There have been many variations on this recipe both interms of mixing ratios and in terms of temperature.

Because of the importance of this particle removal step in thesemiconductor industry, there has been a lot of research on themechanism of this particle removal step. This chemistry can even be usedwithout mechanical particle removal mechanism added. It is now widelyaccepted that, in case when there is no mechanical particle method addedto the chemistry, and therefore, when particle removal is achieved bychemical contacting only, then the contacting chemistry simply removesparticles due to underetching of the particle. A particular goodpublication on this mechanism was written by Hiroyuki Kawahara, K.Yoneda, I. Murozono and T. Tokokoro, “Removal of Particles on Si Wafersin SC-1 solution”, IEICE Trans. Electron., Vol. E77-C, No. 3, March1994, p. 492. The underetching theory goes as follows: a controlledamount of the surface layer is uniformly removed or etched all over thesurface of the wafer to be cleaned. When etching this surface layer, thematerial underneath the particle is also etched away and this etchingreleases the particle from the surface. Then, the particle is washedaway.

Since the current state of the art for removing particles by chemicalmeans only, relies on undercut etching, and since etching increases withtemperature, everyone so far has found that particle removal efficiencyincreases with temperature. M. Meuris et al., Microcontamination, May1992, p. 31, e.g. showed the effect of temperature on etching rate.Therefore, SC-1 solutions are usually used at elevated temperatures.Increased etching can also be achieved by using higher chemicalconcentration. If the etching is too excessive for the device orsubstrate at hand, then sometimes the temperature is lowered, but theparticle removal efficiency is then reduced as well.

In the prior art, when SC-1 solutions are used without any mechanicalparticle removal method, i.e. by chemical contacting alone, thetemperatures used always range from room temperature up to about 80° C.If there is no reliance on the chemical undercutting and when relying ona mechanical method to remove particles instead, then the hightemperature is not needed. For example, when using SC-1 together withmegasonics to remove particles, the SC-1 or any alternative high pHchemistry, merely serves to prevent particles from re-depositing. Whenusing megasonics, the particles are removed by the megasonics vibrationthrough the formation of cavitation events and are prevented fromreattaching to the surface by the high pH of the SC-1 chemistry oralternative high pH chemistry.

Since megasonics relies on cavitation to remove particles and sincecavitation is not very much temperature dependent, but very dependent onthe dissolved gases, it has been found that megasonics and SC-1 combineddon't remove any particles when there are no gases present. It ispossible to create cavitation without any dissolved gases present, socalled vacuum cavitation, but this is only possible at very high powerlevels. Hence, at normal power levels, typically 10-100 W, there is nogaseous cavitation when there are no dissolved gases present and hencethere is virtually no particle removal efficiency when using megasonicswithout any gases dissolved. In R. Gouk, J. Blocking, S. Verhaverbeke,“Effects of Cavitation and Dissolved Gas Content on Particle Removal inSingle Wafer Wet Processing”, in Proceedings of Semiconductor Pure Waterand Chemicals Conference (SPWCC) 2004, Santa Clara, Calif., 2004, it isshown that at 925 kHz and for power levels up to 0.15 W/cm²(corresponding to 100 W on a 300 mm wafer), there is absolutely noparticle removal efficiency for dissolved gas levels of 30 ppb O₂. Onlyfor power levels starting at 0.3 W/cm² (200 W), the particle removalefficiency starts to become non-zero (20%). However, even at only 100 Wand with 300 ppb of dissolved gas (O₂ in this case), the particleremoval efficiency is 90%. This shows clearly the effect of dissolvedgas on the particle removal efficiency due to the cavitation ofdissolved gas bubbles.

Currently, a cleaning paradox has emerged. Megasonics vibration workswell for removing particles and with a very wide temperature range, butthe cavitation which the megasonics produces, and which is used toremove particles, also damages the fine patterns on the wafers. Indeed,the patterns on the wafer are becoming so small that they are very tofragile and are very prone to mechanical damage. This started to be aproblem when the pattern size on the wafers decreased to a size smallerthan 0.3 μm in width or at least in 1 dimension. Initially it wasaddressed by lowering the megasonics power, but now with pattern sizessometimes as small as 22 nm in 1 dimension, any megasonics power orrather any cavitation will destroy such patterns.

Therefore, a new method for removing small particles from the front sideof the wafer without damaging the fragile structures is necessary. Theunderetching mechanism, which does not damage the fragile structures,however can also not be used anymore, since the devices are so small,that underetching would remove valuable material from the surface of thedevice and hence the device characteristics would be degraded. This isthe current cleaning paradox that we are faced with.

This is the case, because the current generations of small devices havethe active device region extremely close to the top surface. This isvery clearly shown for the case of semiconductor wafers and devices madeon such wafers, in the publication by F. Arnaud, H. Bernard, A.Beverina, E. El-Frahane, B. Duriez, K. Barla and D. Levy, “AdvancedSurface Cleaning Strategy for 65 nm CMOS device PerformanceEnhancement”, Solid State Phenomena Vols. 103-104 (April 2005) pp.37-40. In this publication, F. Arnaud et al. clearly show that reducingthe underetching enhances the transistor characteristics.

Hence the paradox: mechanical particle removal cannot be used anymorefor small particle removal, since it also damages the fine patterns, andconventional chemical particle removal by underetching cannot be usedanymore, because of loss of surface material which is now a substantialpart of the device.

Even in those cases where the substrate is completely flat and wheredamage is not a paramount concern, it has been found that for very smallparticles, the mechanical methods are not effective anymore. This isshown in G. Vereecke, F. Holsteyns, S. Arnauts, S. Beckx, P. Jaenen, K.Kenis, M. Lismont, M. Lux, R. Vos, J. Snow and P. W. Mertens,“Evaluation of Megasonic Cleaning for sub-90 nm Technologies”, SolidState Phenomena Vols. 103-104 (2005) pp. 141-146. Mechanical methods toremove particles, such as, but not limited to, brush scrubbing, sprayaerosol bombardment, and ultrasonic and megasonic vibration, are veryeffective for the large particles, i.e. for particles >90 nm, but looseefficiency for the very small particles, <90 nm. Hence, there is a needfor an improved chemical method to remove these very small particleseven on substrates without exposed patterns. This is true for waferswith devices on them after CMP (Chemical Mechanical Polishing). Indeed,these wafers contain parts of the device already on them, but have beenflattened or polished without removing all of the layers in order tomake it easier for photolithography to pattern the next layer. On suchwafers, very small particles are difficult to be removed withconventional mechanical techniques. Gross etching on such polishedwafers is not possible, since then the layers which are exposed would beetched away. These layers will become part of the device later andcannot be etched substantially.

As a summary, there is a great need in the semiconductor industry for asolution and a method and an apparatus that can remove small particlesfrom the front side or back side of semiconductor wafers withoutdamaging the fine patterns and without substantial underetching of thesurface material. There is a general need for an improved chemicalmethod to remove very small particles (<90 nm) even on substrateswithout pattern such as wafers with partial devices after chemicalmechanical polishing.

More generally, none of the presently known methods can removeefficiently very small particles, since most of the mechanicaltechniques loose efficiency for small particles and most of thecurrently known chemical methods are not very effective for very smallparticles. The prior art does not provide for an improved chemicalmethod to remove very small particles more efficiently than theubiquitous SC1 solution for wafers with partial structures or layers onthem.

BRIEF SUMMARY OF THE INVENTION

Briefly, the present invention is a method and cleaning solution forcleaning an electronic substrate, such as a semiconductor wafer, as partof the device manufacturing process. The method comprises the steps ofcontacting a surface of the electronic substrate that has partialstructures or patterns (electronic structures) of a device exposed witha cleaning solution comprised of a polycarboxylate polymer, ethoxylatedpolyamine or an ethoxylated quaternized diamine; and then removing thecleaning solution from the surface. Additional optional steps in themethod include applying acoustic energy to the cleaning solution andfollowing the cleaning by rinsing the surface with a rinsing solutionwith or to without the application of acoustic energy to the rinsingsolution.

The cleaning solution of this invention for removing submicron particlesfrom the surface and/or the bevel of an electronic substrate such as awafer with partial device structures or patterns contains apolycarboxylate polymer, ethoxylated polyamine or an ethoxylatedquaternized diamine. The polycarboxylate polymer of the presentinvention comprises homopolymers or copolymers of acrylic acid,methacrylic acid, maleic acid, fumaric acid, itaconic acid, and thelike.

The cleaning solution which either contains a concentratedpolycarboxylate polymer or a concentrated ethoxylated polyamine or bothand may also additionally contain a base or an acid, can be delivered inconcentrated form and then diluted at point of use and then dispensed orcontacted on the surface or the bevel of an electronic substrate such asa wafer as part of the manufacturing of devices on such wafers. Thedispensing and/or cleaning and/or rinsing optionally can be carried outat subambient temperatures. A base such as ammonium hydroxide,tetramethylammonium hydroxide, choline can be added and in addition oralternatively, an amine such as monoethanolamine and a biocide can beadded. Alternatively or in addition, a surfactant and/or a sequesteringagent can be added.

After dilution or even undiluted, any of the cleaning solutions of theinvention can be used in a method to clean the surface of an electronicsubstrate such as a wafer as part of the manufacturing of devices onsuch wafer.

The cleaning solution can also be used to clean the bevel of theelectronic substrate such as a wafer. The bevel can be cleaned with e.g.a brush or a megasonic nozzle together with the solution of thisinvention.

After cleaning the surface or the bevel with any of the cleaningsolutions of this invention, the cleaning solution needs to be rinsedfrom the wafer and/or bevel surface. The rinsing step can also beassisted with a spray or with megasonics, without causing damagingcavitation if fragile structures are present on the surface. Thedamaging cavitation can be avoided by either not using dissolved gas orby using high frequency megasonics.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The invention is best understood from the following detailed descriptionwhen read in connection with the accompanying drawings. It is emphasizedthat, according to common practice, the various features of the drawingare not to scale. On the contrary, the dimensions of the variousfeatures are arbitrarily expanded or reduced for clarity. Included arethe following figures:

FIG. 1 is a schematic diagram of a single wafer spin-spray systemaccording to the present invention for removing small particles from thefront side of the wafer;

FIG. 2 is a schematic representation of a nozzle where the solution ofpolycarboxylate polymer or ethoxylated polyamine is accelerated by an N₂or CDA gas flow outside the nozzle body;

FIG. 3 is a schematic diagram of a single wafer spin-spray system of apreferred embodiment of the present invention for removing small andlarge particles from the front side of the wafer; and

FIG. 4 is a schematic top view of various transducers that can be usedin the preferred embodiment shown in FIG. 3, positioned below the wafer.

DETAILED DESCRIPTION OF THE INVENTION

A cleaning solution used in the present invention comprises apolycarboxylate polymer solution. In one embodiment, the polycarboxylatepolymers may comprise homopolymers or copolymers of acrylic acid,methacrylic acid, maleic acid, fumaric acid, itaconic acid and the like.When the term homopolymer is used, it is intended that it includes bydefinition, polymers that may contain quantities of about 20 molepercent or less, of one or more comonomers. In other words, a polymercontaining up to 20 mole percent of comonomers will still be considereda homopolymer. The cleaning solution may also comprise a blend of theabove polycarboxylate polymers.

Particularly suitable polycarboxylate polymers are prepared frommonomers having the general formula (Formula 1):

Where R1 and R2 is either a hydrogen atom (H) or methyl radical (CH₃,also represented by Me).

A polycarboxylate polymer (homopolymer) formed from monomers of thistype can be schematically represented by the following formula (Formula2):

where R1 may be H or COOH (carboxyl); and R2 may be H, Me or CH₂COOH.

In specific embodiments, the monomer may be acrylic acid (R1 and R2 areH) or methacrylic acid (R1=H and R2=Me). In other embodiments, themonomers may be maleic acid (R1=COOH and R2=H, with the carboxylic acidgroups in the cis configuration); fumaric acid (R1=COOH and R2=H, withthe carboxylic acid groups in the trans configuration); and itaconicacid (R1=H and R2=CH₂COOH). Polycarboxylate polymers (copolymers)comprising combinations of these monomer units may also be used (e.g.Formula 5, below).

Other suitable polymers are a maleic/olefin copolymer. This embodimentof the polycarboxylate polymer comprises a copolymer derived from maleicanhydride and a lower olefin. Preferably the maleic anhydride monomerhas the following formula (Formula 3):

where R1 and R2 are independently H, an alkyl or a phenyl group. Mostpreferably R1 and R2 are H. The lower olefin component is e.g. ethylene,propylene, isopropylene, butylene or isobutylene and most preferablyethylene. This maleic/olefin copolymer can be added to a suitableacrylic acid or methacrylic acid homopolymer or copolymer. Themaleic/olefin copolymer has the formula (Formula 4):

Other suitable polycarboxylate polymers are polymaleic acids, i.e.homopolymers of maleic acid. Still other suitable polycarboxylatepolymers are acrylic acid/maleic acid copolymers which can berepresented schematically by the following formula (Formula 5):

Formula 5 is a copolymer of polyacrylates and polymaleates. In theschematic representation above, the first group is an acrylate group andthe second group is a maleate group.

An acrylic homopolymer can be schematically represented by the followingstructure (Formula 6):

The average molecular weight of the polycarboxylate polymers given byFormulas 1-6 can vary between 300 and 1000000 Dalton. Preferably theaverage molecular weight is between 500 and 200000, even more preferablybetween 1000 and 80000 and most preferably between 2000 and 10000.

A particularly good copolymer for use in the present invention is a50/50 acrylic/maleic copolymer (Formula 5) with an average molecularweight of about 3000 Dalton.

Such an acrylic acid/maleic acid copolymer or an acrylic homopolymer ora polycarboxylate polymer in general is typically synthesized by a rawmaterial supplier and is typically made available in either the acidform or in a neutral form where the acid carboxylic groups areneutralized by a cation, most often Na⁺ (sodium). The acid form ispreferable to use as the starting raw material for the cleaning solutionblend. In the above schematic representations of the polymers, typicallythe acid form is shown. For the Na⁺ neutralized form, the CO₂H group inthe formula above should be replaced by a CO₂Na group.

For the cleaning solution of this invention, water soluble salts ofcarboxylic polymers as described above are especially preferred.Alternatively an ester of the carboxylic polymers can be used. The watersoluble salt can be preferably an ammonium or substituted (quaternary)ammonium salt. For semiconductor wafer cleaning, an alkali free solublesalt is preferred. The carboxylic polymers are converted to the desiredsalt by reaction of the acid form with the appropriate base. A typicalalkali free soluble salt can be made by reaction of the polymer in theacid form with e.g. ammonium hydroxide, tetramethylammonium hydroxide orcholine. Alternatively the ester form can be reacted with theappropriate base.

Typically the polycarboxylate polymer of this invention is added to abase in concentrated form at the chemical solution blending plant. Mostoften the base will be NH₄OH for semiconductor cleaning, but it can alsobe TMAH (Tetra Methyl Ammonium Hydroxide) or choline or any other basethat is suitable for the semiconductor cleaning operation. Forsemiconductor wafer cleaning, this concentrated base solution with thepolycarboxylate polymer can be used as a direct replacement for theNH₄OH in the ubiquitous SC1 solution. This concentrated solution is thentypically shipped to the manufacturing plant where the cleaningoperation will be performed. At this manufacturing plant, theconcentrated solution will be diluted with H₂O and or other chemicals tomake up the cleaning solution. However, the polycarboxylate polymer canalso be shipped in the acid form and then the base gets added at thesemiconductor cleaning plant.

Alternatively to the polycarboxylate polymers, an ethoxylated polyaminecan be used in a cleaning solution to remove particles. Schematically,an ethoxylated polyamine for use according to this invention has thefollowing general formula (Formula 7):

where EO is the oxyethylene moiety (—CH₂CH₂O—). The preferred ranges areas follows: the value of x ranges from 1 to 100, the value of n rangesfrom 1 to 30 and the value of m ranges from 1 to 30. The last EO istypically terminated with H (not shown in the schematic formula). Aparticular useful ethoxylated polyamine is the ethoxylated pentaminewhere x=15, n=2 and m=4. Schematically, the structure of the ethoxylatedpentamine, which is very useful for the current invention, is as follows(Formula 8):

Another useful compound for use in the current invention is theethoxylated, quaternized diamine with the following structure (Formula9):

The ethoxylated polyamine of this invention will typically be added inconcentrated form to make up a chemical solution in the blending plant.Typically the ethoxylated polyamine will be blended into either aneutral solution or an acidic solution.

Both the polycarboxylate polymer solution and the ethoxylated polyaminecan be supplied as a concentrated solution without base. However, whenusing the polycarboxylate polymer solution for cleaning semiconductorwafers, the final blended cleaning solution is typically used atalkaline pH values, preferably in excess of pH 8. Ammonium hydroxide orother bases are typically added to increase the pH of the solution. Thiscan be done at the chemical manufacturing or blending plant, but it canalso be done at point-of-use. The ethoxylated polyamine on the otherhand can be used over a wide pH range and is not limited to alkaline pHcleaning when using this for cleaning semiconductor wafers. Finally,Surfactants and chelating agents can also be added.

In addition, in order to make up a cleaning solution for semiconductorwafers, H₂O₂ can be added to make an analogue of the omnipresent SC-1solution. The addition of H₂O₂ is useful to avoid any Si surface etchingon such wafers, as is known in the prior art. The H₂O₂ preferably isadded at point-of-use, whereas the other components can be blendedtogether at the chemical blending plant.

The ammonium hydroxide with the polycarboxylate polymer with or withoutperoxide added is a superior cleaning solution to the conventionalammonium hydroxide and peroxide solution for wafers with partialstructures, layers or patterns to make finished devices on such wafers.It can remove very small particles <90 nm and can remove particles evenwithout any mechanical removal technique added. This is very importantfor wafers which have fragile structures exposed to the cleaningsolution.

After dilution of the source solution in the fab for cleaning use, thefinal concentration of the polycarboxylate polymer in the cleaningsolution for cleaning the substrates is preferably between 0.001%-6% byweight. More preferably the concentration of the polycarboxylate polymerin the cleaning solution is between 0.01% and 2% and most preferably thepolycarboxylate polymer in the cleaning solution is between 0.1% and 1%by weight. A particular good and effective concentration is about 0.6%for fast particle removal, but the cleaning effect of thepolycarboxylate polymer on semiconductor wafers can even be observeddown to 0.001%. There is a trade-off between concentration and cleaningtime. At lower concentration the cleaning effect of the polycarboxylatepolymer can be observed at longer cleaning times, whereas at higherconcentration, even for short contacting times, the cleaning effect isalready clearly seen.

When using the ethoxylated polyamine for cleaning semiconductor wafers,the concentration ranges for the ethoxylated polyamine are preferably atconcentrations between 0.001% and 5% and more preferably between 0.01%and 2% ad most preferably between 0.1% and 1% by weight.

Typically, the polycarboxylate polymer or the ethoxylated polyamine canbe supplied to the fab in a concentrated solution, which can then bediluted with DI water and with other chemicals at point-of-use orcentrally in the fab to yield the final cleaning concentration. Thepolycarboxylate polymer in a concentrated source solution can besupplied close to its solubility limit in such a source solution inorder to reduce transportation expenses, but substantially lowerconcentrations can be used as well e.g. to suppress raw material costsand hence to reduce the final sales price of the blended chemical. Otherreasons to supply a lower concentration is e.g. if the fab is usingequipment that is set up for diluting the source concentration in apre-fixed dilution ratio. E.g. typical dilution ratios used in fabs are5 times such as used e.g. in a 5:1:1 SC-1 bath. In that case, thepolycarboxylate polymer concentration, when supplied together with theNH₄OH in 1 solution, will need to be substantially lower in the sourcesolution in order to give the right concentration after dilutingaccording to such a pre-fixed ratio. Alternatively, the fab may not beset up to handle any dilution and will require the cleaning solutionsupplied at the use concentration. The solubility of the polycarboxylatepolymer depends on its molecular weight. For this invention,polycarboxylate polymers with a molecular weight between 300 and1,000,000 Daltons can be used. Higher molecular weight polycarboxylatepolymers will be less soluble than lower molecular weightpolycarboxylate polymers. Average molecular weight numbers (3000-70,000Daltons) will typically have a solubility of about 40-60%-w in water.Therefore generally the solution can be supplied to the fabin-concentrations ranging anywhere from 0.001% to 60%.

Ethoxylated polyamines are substantially less soluble. The ethoxylatedpentamine e.g. has a solubility of around 5%-w in water.

Typically the source solution as supplied by the chemical blendingoperation will be used in the fab for cleaning either straight (i.e.undiluted), or diluted, but diluted with water and/or other chemicals ispreferable for economic reasons. It is clear that transporting aconcentrated solution and diluting it at point-of-use with local DIwater is more economical than diluting at the chemical blending companyand then transporting the diluted solution over long distances.

When diluting the source solution, dilution ratios will be preferablybetween 5 and 10,000 times with DI water to make up the substratecleaning solution, more preferably 5 to 1000 times, and most preferably5 to 100 times. Besides dilution with water, other chemicals can beadded as well.

When ammonium hydroxide is added to the concentrated source solution tomake a source solution containing polycarboxylate polymer and ammoniumhydroxide, it can be added in a concentration range of 1%-28%-w (weightof NH₃) to make a source solution consisting of ammonium hydroxide andpolycarboxylate polymer. This then can easily replace the now commonlyused ammonium hydroxide source solution in fabs to clean wafers with thecommon SC-1 solution. But any other suitable base can be used instead ofammonium hydroxide for making up the source solution.

The source solution may also contain from 0.01% to 40% of an organicamine. Suitable organic amine compounds may be selected fromalkanolamines (e.g. primary alkanolamines: monoethanolamine,monoisopropanolamine, diethylethanolamine, ethyl diethanolamine,secondary alkanolamines: diethanolamine, diisopropanolamine,2-(methylamineo)ethano, morpholine, ternary alkanolamines:triethanolamine, tri-isopropylamine), alkylamines (e.g. primaryalkylamines, monomethylamine, monoethylamine, monopropylamine,monobutylamine, monopentylamine, cyclohexylamine, secondary alkylamines:dimethylamine), alkyleneamines (e.g. primary alkylene amines:ethylenediamine, propylenediamine, triethylenetetramine), and mixturesthereof. Preferred examples of such materials include monoethanolamine,ethylenediamine, triethylenetetramine and mixtures thereof. The mostpreferred is monoethanolamine. The amount of the organic aminepreferably ranges from 0.01% to 20%, and most preferably from 0.2% to2%.

The source solution may also contain a biocide such as2-Methyl-4-isothiazolin-3-one (MIT) or 2-Methyl-4-Isothiazolin-3-oneHydrochloric acid (C4H4NOS, HCl), (MIHCA). The concentration of thebiocide is preferably from 1 ppm to 100 ppm, and more preferably form30-70 ppm. Other biocides may be used as well. Biocides do not improvethe particle removal efficiency but prevent any bacterial growth in thechemicals.

Surfactants can also be added. Typically non-ionic surfactants arepreferred. Preferred surfactants are the ethylene oxide type surfactantswith a general structure C_(n)H_(2n+1)O(C₂H₄O)_(m)H. A typical non-ionicsurfactant is C₁₂H₂₅O(C₂H₄O)₁₁H. The concentration of the surfactant inthe concentrated source solution will be preferably between to 0.1% and5%. Most preferably concentrations are around 0.5% for the concentratedsource solution. The concentration after dilution with water and whenused for cleaning the surfaces will be preferably between 0.0001 to 0.5%by weight. This is between 1 ppm and 5000 ppm by weight. More preferablythe concentration after dilution will be between 10 ppm and 500 ppm.Surfactants do not substantially improve the particle removalefficiency, but may be added for other reasons, such as for wettingpurposes when the surface is hydrophobic.

Sequestering agents or complexing agents can also be added. Sequesteringagents do not substantially improve the particle removal efficiency, butcan be added to prevent metallic impurity deposition on the wafersurface. Preferred sequestering or complexing or chelating agents arcthe nitrogen-containing carboxylic acids such asethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaaceticacid (DTPA). The concentration of the sequestering agent after dilutionwith water and when used for cleaning the surfaces will be preferablybetween 10 ppm and 500 ppm.

The solutions of this invention with polycarboxylate polymers removeparticles substantially better than the conventional ammonium hydroxideonly solutions, such as the ubiquitous SC1 solution or other solutionsknown in the prior art for cleaning wafers with partial structures orpatterns of devices on them.

The solution with polycarboxylate polymers or ethoxylated polyamineswith or without amines, surfactants and or sequestering agents and otherchemicals added can be contacted on the substrate of the wafer in a bathor immersion type apparatus, which can be single substrate or batch, orin a spinning wafer type apparatus, which can also be single substrateor batch or in a horizontal conveyor belt style apparatus or in anyother apparatus type suitable for contacting one or more substrates witha solution with polycarboxylate polymers or ethoxylated polyamines withor without NH₄OH or other chemicals added and with or without amines,surfactants and or sequestering agents added.

Finally, it is clear that other substances may be added to the solutionwith polycarboxylate polymers with or without NH₄OH or any other base.Adding other substances to this solution does not constitute a deviationfrom the idea of the current invention. Specifically H₂O₂ may be addedto the solution.

The removal efficiency of more tenaciously adhered particles on thesurface can be improved from the simple contacting with apolycarboxylate polymer or ethoxylated to polyamine containing solutionof this invention in several ways.

Such known additional ways include, for example, megasonics, an aerosolspray and a scrubbing action with a PVA brush. Indeed, the megasonicsact by causing cavitation events due to the dissolved gases in thesolution. These cavitation events cause a mechanical agitation on theadhered particles and hence dislodge them from the surface of the wafer.The megasonics also act by reducing the boundary layer. An aerosol spraytechnique exerts a mechanical force onto adhered particles by causing avery fast flow of liquid over the surface of the wafer. An aerosol spraytechnique can be set up such that it only exerts a force on largeparticles and large features. Hence, an aerosol spray technique can beselective for exerting a force on large particles and large features,but not on small particles and small features, which are very fragile.An aerosol spray technique also reduces the boundary layer in a similarway like the megasonics.

In addition, after the cleaning is finished, it is advantageous tofollow up the cleaning sequence with an improved DI water rinse. Theimproved DI water rinse can consist of a megasonics without gas to avoidcavitation or a megasonics at high frequency. The improved DI waterrinse can also be a rinse with a spray. A spray rinse can be a regularwater spray or an aerosol spray. A regular water spray is effective athigh flows; typically a flow in excess of 1 L/min for a 300 mm sizedsubstrate such as a semiconductor wafer is very effective.

The temperature of the cleaning solution during cleaning of wafers canbe any temperature from 0 degrees C. to 100 degrees C. with roomtemperature preferred because of its ease and economical advantage. Forabsolute best particle performance lower temperatures are evenpreferred. Preferred temperatures for best particle performance arebetween 1 degrees C. and 20 degrees C. and more preferred from 3 degreesC. to 15 degrees C. and most preferred from 5 degrees C. to 12 degreesC. Lower temperatures are also advantageous to reduce the surfaceetching amount, which is often undesirable as it removes active materialfrom semiconductor structures, part of the devices present on thewafers. At lower temperatures a higher pH can be used with equivalentetching amount as one would have at a higher temperature, but at aconsiderable lower pH. The higher pH is improving the cleaningperformance. The subsequent rinsing can also be carried out atsubambient temperatures to improve the particle performance.

After cleaning with the solution of the current invention containingeither a polycarboxylate polymer or an ethoxylated polyamine, it isdesirable to remove all of the polycarboxylate polymers, or all of theethoxylated polyamines. Normally this can be done adequately by thoroughrinsing. If absolutely the lowest levels of remains are necessary,especially after using the polycarboxylate polymer solutions, then a twostage cleaning can be used. The first stage is a NH₄OH based clean, suchas an SC-1, or simply an NH₄OH based rinsing. The second stage is an HClbased cleaning, such as SC-2, or simply HCl rinse water can be used.Alternatively the NH₄OH based step can be skipped and the rinsing can beacidified with HCl. This is particularly useful for the ethoxylatedpolyamine solutions.

For purposes of illustration, the principles and methods of the presentinvention for a concentrated solution and a cleaning solution and amethod and apparatus for cleaning the front side of the wafer and/or theback side of the wafer and/or the bevel of the wafer will now bedescribed.

A typical make-up of a concentrated source solution according to theinvention for use in a 5:1:1 SC-1 solution and when the copolymer issupplied together with the NH₄OH as one blended source solution is shownin Example 1:

Percent (%) 50/50 acrylic/maleic copolymer in 3.5%-w the acid form withan average molecular weight of 3000 Daltons NH₄OH (26%-w as NH₃) Balance

This concentrated solution can be made off-site and be transported tothe fab. In the fab, it is typically diluted with water with a factor5:1:1 H₂O:H₂O₂(30%):concentrated solution of Example 1 to a finalcleaning concentration of 3.7% NH₄OH (as NH₃), 0.5% acrylic/maleiccopolymer and 4.3% H₂O₂. H₂O₂ is typically be added in such cleaningsolutions in the same or higher amount as NH₄OH. It has to be remarkedthat the pH of these final solutions will be slightly less than whatwould be obtained without the 50/50 acrylic/maleic copolymer (in theacid form) since the 50/50 acrylic/maleic copolymer contains acidiccarboxylic groups. One can compensate for that by using the appropriateslightly higher amount of the source solution to end up with the samefinal pH as one would have when using a conventional 5:1:1 solution madeup of NH₄OH:H₂O₂:H₂O. In the case of a 5:1:1 solution, this differenceis however negligible. This compensation is not necessary if the 50/50acrylic/maleic copolymer would be supplied in a neutral form. The finalNH₄OH concentration at 26%-w will be slightly lower than the 28%-w as ismore common, when the copolymer will be added already dissolved in waterto 28%-w standard solution. When the copolymer will be added in solidform, the 28-w% concentration can be maintained closer.

A typical make-up of a concentrated solution according to the inventionfor use in a 20:1:1 or a 20:1 solution is shown in Example 2:

Percent (%) 50/50 acrylic/maleic copolymer 12%-w in the acid form withan average molecular weight of 3000 Daltons NH4OH (21%-w as NH3) Balance

This concentrated solution of Example 2 can be made off-site and betransported to the fab. In the fab, it is typically diluted with waterwith a factor 1:20 to a final cleaning concentration of 1% NH₄OH (asNH₃) and 0.6% acrylic/maleic copolymer. H₂O₂ can also be added. H₂O₂would typically be added in the same or higher amount as NH₄OH to make a20:1:1 solution H₂O:H₂O₂:source solution of Example 2. In this case, dueto the acidifying effect of the acrylic/maleic copolymer (when suppliedin the acid form), the pH of a 20:1:1 H₂O:H₂O₂:source solution ofExample 2 is in a similar range as the pH of a 20:1:0.3 solution ofH₂O:H₂O₂:NH₄OH (28% NH₃). One can compensate for that if desired bydecreasing the H₂O₂ concentration or by increasing the concentration ofthe source solution of Example 2.

A typical make-up of a concentrated solution according to the inventionfor use in a 30:1 or a 30:1:0.22 solution is shown in Example 3:

Percent (%) 50/50 acrylic/maleic copolymer 15.6%-w in the acid form withan average molecular weight of 3000 Daltons NH4OH (19%-w as NH3) balance

This concentrated solution of Example 3 can be made off-site and betransported to the fab. In the fab, it is typically diluted with waterwith a factor 1:30 to a final cleaning concentration of 0.64% NH₄OH (asNH₃) and 0.5% acrylic/maleic copolymer. H₂O₂ can also be added. In orderto get the same pH as one would get for a 30:1:1 conventional H₂O:NH₄OH(28%):H₂O₂ (30%) solution, H₂O₂ would typically be added in the same orhigher amount as the free NH₄OH which is not used to neutralize thecopolymer, when the copolymer is added in the acid form. That would bethe case for a mixing ratio of about 30:1:0.22 or alternatively said amixing ratio of 136:4.5:1 for H₂O:concentrated solution of example 3:H₂O₂ (30%). The concentration of the H2O2 may also be doubled e.g. toroughly a 70:2:1 H₂O:concentrated solution of example 3: H₂O₂ solution.This will have a pH comparable to a conventional 30:1:2 H₂O:NH₄OH:H₂O₂solution.

A typical make-up of a concentrated solution according to the inventionis shown in Example 4:

Percent by volume (%) 50/50 acrylic/maleic copolymer 15% in the acidform with an average molecular weight of 3000 Daltons TMAH  5% WaterBalance

This concentrated solution can be made off-site and be transported tothe fab. This solution can be diluted in the fab with water and/or otherchemicals. Typically this solution can be used to clean Cu/Low K or ingeneral Cu wafers. Because of the pH of this solution, this solutionwill grow a thin passivating oxide on Cu. In many cases this isdesirable to stop uncontrolled oxidation of metallic Cu.

Typically, pH ranges between 8 and 14 and preferably between 9 and 12and most preferably between 10 and 11 are very good for cleaningparticles in combination with the acrylic/maleic copolymer or theacrylic homopolymer or any polycarboxylate polymer in general. Othersubstances can be used instead of NH₄OH to get a similar pH. Typicalother substances used to increase the pH are e.g. TMAH (as in example 4)and choline.

An example of a single wafer spin-spray cleaning chamber will now begiven in more detail. Referring to FIG. 1, the spin chamber 20 containsthe wafer 21, being held horizontally by a wafer holder 22, connected toa motor 23. The wafer is held with the front side of the wafer facingdown. The motor and wafer holder assembly is mounted in a bowl 24containing a liquid diverter 25, an exhaust 26 and a drain 27. A nozzle28 is mounted to direct the liquid solution with the acrylic/maleiccopolymer or acrylic homopolymer preferably at ambient or subambienttemperature onto the spinning wafer 21. The nozzle 28 is directed todispense the liquid from below the wafer while the wafer is facingfront-side down. In this way, gravity helps in transporting, theparticles away from the surface, out of the boundary layer and into theflowing stream. The nozzle 28 is fed from a mixer 29 where a solution ofacrylic/maleic copolymer or acrylic homopolymer and NH₄OH and DI wateris mixed in the desired ratio. The solution is fed from line 30. Thechiller 32 may cool the incoming DI water from line 33 down to a desiredsubambient temperature. In addition to the nozzle 28, which can supplysubambient temperature liquid onto the spinning wafer, another nozzle(not shown) can be used to supply an accelerated atomized aerosol of thesolution onto the wafer. This accelerated nozzle helps in bringing thesolution in close proximity to the adhered particles on the wafer.

A close up of such a accelerated atomized aerosol nozzle configurationis shown in FIG. 2. Referring to FIG. 2, a nozzle 100 is shown withnozzle body 103 and liquid inlet 101 for the solution withacrylic/maleic copolymer or acrylic homopolymer. Inlet 102 is the gasinlet. A variety of accelerating gases can be used, but mostconveniently N₂ or CDA (Compressed Dry Air) can be used. The liquidinlet 101 is connected to the liquid outlet 106. The gas inlet 102 isconnected to gas outlets 104 and 105, which can be a single circularoutlet. The gas coming out of outlets 104 and 105 atomizes andaccelerates the atomized droplets 108 of the liquid coming out of outlet106. The atomized aerosol containing acrylic/maleic copolymer or acrylichomopolymer is jetted towards the wafer surface.

Even though the chiller 32 in spin chamber 20 is positioned before themixer 29, the mixing of acrylic/maleic copolymer or acrylic homopolymerand DI water can be done before the chiller. Even though in FIG. 1, theatomized aerosol is supplied with a solution of acrylic/maleic copolymeror acrylic homopolymer, the aerosol can also be supplied with simple DIwater. In this case the aerosol is merely used to create a motion in thesolution already on the wafer or the aerosol jet is used to remove largeparticles selectively as is known in the prior art.

After the wafer contacting with a solution of acrylic/maleic copolymeror acrylic homopolymer, the wafer can preferably be rinsed withsubambient temperature DI water. Indeed, the rinsing of the wafer withsubambient temperature DI water will reduce the final particle count.The drying can be done with any of the known methods for drying wafers.In batch mode the most preferred drying method is the surface tensiongradient method, preferably using a vapor of IPA. However, a spin drymethod can also be used. In a single wafer mode a surface tensiongradient drying method can be used or a simple spin dry method can beused. Any other method to dry a substrate without adding substantialcontamination during the process of drying, i.e. any known clean dryingmethod, can also be used. If a surface tension gradient drying method isused, a vapor of IPA will be blown in the center of the wafer, while thewafer is facing front-side down. This IPA nozzle is not shown in FIG. 1.

Even though the simple act of contacting the surface of a wafer with asolution of acrylic/maleic copolymer or acrylic homopolymer can removesubmicron particles very effectively, the removal efficiency can beimproved with an accelerated jet, and it can also be done by the use ofmegasonics. One such apparatus, a single wafer spin-spray tool, is shownin FIG. 3. In the single wafer spin-spray apparatus 40 of FIG. 3, awafer holder 42 connected to a motor 43 holds a wafer 41. The wafer canbe held with the front side of the wafer facing down. Positioned belowthe wafer is a sonic transducer 48. The sonic transducer is e.g. made ofstainless steel or aluminum and is preferably coated with PFA. On thebackside of the sonic transducer, PZT crystals 49 are bonded to generatethe sonic waves. The PZT crystals are connected to a megasonic frequencypower supply (not shown) and protected in a housing to isolate the PZTcrystals from the cleaning liquids (not shown). Closer to the center ofthe wafer, there is a liquid feed through 51, which is connected to achemical feed line 50. This chemical feed line supplies chemicals or DIwater through the sonic transducer 48 to the backside of the wafer 41.The PZT crystals 49 generate the sonic waves in a frequency range of200-6000 kHz. Conventionally frequency ranges between 700 kHz and 1.8MHz are being used. This is commonly used for megasonics cleaning.However, any frequency range of 200-6000 kHz can be used.

The wafer 41 with wafer holder 42, motor 43 and sonic transducer 48 ismounted inside a bowl 44 with liquid diverter 45, drain 47 and exhaust46. The sonic transducer 48 can have various shapes as is shown in FIG.4. In FIG. 4, a linear transducer 60, a full wafer disk shapedtransducer 70 and a pie-shaped transducer 80 are shown. In eachtransducer 60, 70 and 80, the outline of the wafer 41 is shown and thechemical feed through 51 is shown.

The final rinse method is very important, since the final rinse needs toremove all of the acrylic/maleic copolymer or acrylic homopolymer fromthe surface. The final rinse method can be preferably carried out withmegasonics with or without gas to avoid damage, high frequency to avoiddamage. The final rinse can also be carried out with an atomized spray.The final rinse is preferably carried out with subambient temperaturewater.

In addition, the final rinse with subambient temperature water can becombined with a surface tension gradient particle removal and dryingtechnique. Using an IPA vapor of some sort usually generates the surfacetension gradient. The subambient temperature water can be contacted tothe front side of the wafer first, followed by a surface tensiongradient cleaning and or drying.

The solution of the present invention is very useful for bevel edgecleaning. Indeed, the acrylic/maleic copolymer or acrylic homopolymer isvery powerful at removing contamination from the bevel of the wafer.This is best carried out with an aggressive mechanical means that isselective to the bevel itself. The easiest mechanical assist that isselective to the bevel itself is a brush. If the brush material onlycontacts the wafer bevel edge and not the front side of the wafer, thenthis method can remove the contamination from the bevel edge withoutdamaging fragile structures on the front side of the wafer. Finally alast mechanical assist is a sonic energy that is confined to the edge ofthe wafer. The sonic energy will only cause damage when the energy istransferred to the liquid. Hence, the front side of the wafer must bekept dry while applying this sonic energy to the bevel edge of thewafer.

In view of this disclosure, a representative embodiment of the presentinvention is a method for cleaning submicron particles off a surface ofa substrate. The method comprises the step of contacting a surface ofthe substrate with a cleaning solution comprised of a cleaning agent,such as a polycarboxylate polymer, including the polycarboxylatehomopolymers or copolymers described previously with respect to Formulas1-6, or an ethoxylated polyamine or an ethoxylated quaternized diaminedescribed previously with respect to Formulas 7-9). Generally, thesubstrate is an electronic substrate meaning that it is a semiconductorwafer, a storage medium, such as a hard disk, or a substrate used inmanufacturing wafers or storage media, such as a photomask or an imprintmold, or read/write head assembly parts. The method may be used to cleana single substrate or more than one substrate at a time. An optionalstep in the method is to apply acoustic energy to the cleaning solutionwhile the cleaning solution is in contact with the surface. Anotheradditional optional step in the method, and one that is preferred, is toremove the cleaning solution from the surface by rinsing the surfacewith a rinsing solution, such as an aqueous solution, with or withoutthe application of acoustic energy to the rinsing solution while thesurface is being rinsed. In this context acoustic energy means acousticenergy of any appropriate frequency, such as ultrasonic energy ormegasonic energy.

Generally, the surface of the substrate has a plurality of particlesadhered to it and at least some of the particles are carried away fromthe surface when the cleaning solution is removed from the surface, suchas by rinsing. In a particularly useful application, the particles aresubmicron particles, meaning that the particles are smaller than onemicrometer. In another particularly useful application, the surface ofthe substrate has at least one electronic feature having a dimension ofless than 0.3 micrometers formed on it. Examples of such electronicfeatures are the fine patterns on semiconductor wafers, such astransistor gates or interconnect lines formed on the surface of asemiconductor wafer. Other examples include the patterns formed inimprint molds, which are the reverse image of the features on asubstrate, such as a semiconductor wafer, or the features formed on aphotomask that are reduced in the photolithographic process.

Regardless of whether or not the surface of the substrate contains anelectronic feature, the cleaning method of the present invention is anisotropic cleaning method that does not utilize a pad to abrasivelyremove material from the surface of the substrate as is done in aplanarization process, such as CMP.

Another embodiment of the present invention is a cleaning solution forcleaning substrates, including semiconductor wafers and other electronicsubstrates, and that can be used in the method described above. Thecleaning solution comprises a cleaning agent, such as a polycarboxylatepolymer, or an ethoxylated polyamine, or an ethoxylated quaternizeddiamine.

Although the present invention has been described in terms of thepresently preferred embodiments, it is to be understood that suchdisclosure is not to be interpreted as limiting. Various alterations andmodifications will no doubt become apparent to those skilled in the artafter having read the above disclosure. Accordingly, it is intended thatthe appended claims be interpreted as covering all alterations andmodifications as fall within the true scope of the invention.

1. A method for removing particles smaller than one micron from thesurface of a semiconductor wafer having at least one electronic featureformed on the surface comprising, contacting the surface with a cleaningsolution comprised of a polycarboxylate polymer and a base chosen fromthe group consisting of ammonium hydroxide, TMAH and choline, thecleaning solution having a pH of 8 or higher and not including hydrogenperoxide, and the polycarboxylate polymer having a concentration in therange of 0.01% to 2% by weight.
 2. The method of claim 1 wherein thepolycarboxylate polymer comprises either homopolymers or copolymers ofacrylic acid, methacrylic acid, maleic acid, fumaric acid, or itaconicacid.
 3. The method of claim 1 wherein the polycarboxylate polymercomprises a polymer that is prepared from either monomers having thegeneral formula:

where R1 and R2 is chosen from a hydrogen atom or a methyl radical, orfrom monomers having the following formula:

where R1 and R2 are independently H, an alkyl or a phenyl group.
 4. Themethod of claim 1 wherein the polycarboxylate polymer is anacrylic/maleic copolymer.
 5. The method of claim 1 wherein thepolycarboxylate polymer has an average molecular weight between 300 and1,000,000 Dalton.
 6. The method of claim 1 wherein the polycarboxylatepolymer has a concentration in the range of 0.1%-1% by weight.
 7. Themethod of claim 1 wherein the cleaning solution has a pH in the range of9-12.
 8. The method of claim 1 further comprising: after the surface hasbeen contacted with the cleaning solution, removing the cleaningsolution from the surface.